The benefits of network virtualization are well known. VMware® NSX® is a product suite that allows for virtualizing the network for VMs. NSX provides the network elements as fundamental building blocks of a distributed virtual network, elements such as Distributed Logical Switches (for providing L2 based packet forwarding) and Distributed Logical Routers (for providing L3 based packet forwarding).
The notion of a distributed logical network element (e.g., a distributed logical Switch or Router) is powerful since it allows the operator a construct a virtual network while hiding the underlying physical network connectivity and its limitations. The only thing required from the underlying physical infrastructure is that it is capable of forwarding Ethernet encapsulated IP frames.
The distributed logical network element is instantiated on a number of physical nodes (e.g. hypervisors) that participate in the logical network. These nodes also provide uniform packet forwarding capabilities in software. The control plane is responsible in configuring these uniform policies on the participating hypervisor nodes. These policies and configurations are necessarily at the logical level. In other words, they are not concerned with the underlying physical topology. This approach works well where the underlying physical network provides “uniform connectivity” to all participating hypervisors. By “uniform connectivity”, all the hypervisors are connected to a network with similar properties like latency, throughput, etc.